The present invention relates to a deflection yoke for a cathode ray tube and, in particular, to a deflection yoke including a coil having a non-constant distribution of turns.
A deflection yoke for a cathode ray tube (CRT) includes a shaped horizontal coil for deflecting the beam or beams of electrons produced by an electron gun in a horizontal direction across the CRT faceplate (screen) and a shaped vertical coil for deflecting the beam(s) of electrons across the screen in a vertical direction. Typically, many horizontal scans are accomplished at a relatively high horizontal scan rate within each cycle of the relatively low frequency vertical scan rate. The horizontal and vertical deflection coils are usually shaped so as to lie in a generally conforming manner close to and generally surrounding the funnel-shaped glass envelope of the CRT proximate a tube neck that contains the electron gun. The deflection yoke usually has a shaped core of ferromagnetic material, such as a ferrite material, for more effectively concentrating the magnetic field produced by the horizontal and vertical coils in the interior of the tube envelope in a deflection region thereof for deflecting the electron beam(s) in the horizontal and vertical directions.
The inherent problem of deflection yokes is the significant inductance exhibited by the coils in combination with the ferrite core, particularly for the horizontal coil due to its operation at a higher horizontal scan rate or frequency. Such inductance dictates the amount of energy that must be stored in the magnetic field to produce a particular magnetic field strength in the deflection region of the CRT. A measure of the energy stored in the magnetic field produced by the horizontal coil is referred to as the xe2x80x9chorizontal stored energyxe2x80x9d or xe2x80x9cHSExe2x80x9d and is a useful relative measure or parameter for comparing the relative efficiency of different deflection yokes. HSE is a value in milli-Joules (mJ) calculated by HSE=xc2xd L(Ip)2 where L is the inductance of the deflection coil in milli-Henries and Ip is the peak deflection current in amperes.
As certain desirable features of a CRT are pursued, e.g., a xe2x80x9cshortxe2x80x9d or xe2x80x9cslimxe2x80x9d CRT having reduced depth between the CRT faceplate and the far end of the tube neck, greater deflection angles are desired which increases the strength of the magnetic deflection field required. Newer wider CRTs, such as the 16:9 aspect ratio CRTs employed in high-definition television (HDTV) displays, tend also to increase the required deflection angle and the strength of the deflection field required. The foregoing tends to increase the required coil size and/or number of turns and/or drive current magnitude, all of which tend to increase the HSE of the deflection yoke.
Practical considerations, such as heat generation, temperature rise, and the cost of the deflection yoke and of the circuitry employed to apply suitable drive currents thereto, serve to limit the maximum energy stored in the magnetic field to about 7-8 mJ. Conventional deflection yokes employ deflection coils having a xe2x80x9cuniformxe2x80x9d or xe2x80x9cconstantxe2x80x9d turns distribution, i.e. the number of turns producing the magnetic deflection field is substantially the same over a majority of the entire Z-axis length of the yoke, except for relatively small regions at the yoke entrance and yoke exit where the number of turns changes rapidly from zero to the constant number of turns, and for small numbers of correction turns or correction coils for correcting coma, convergence, distortion and the like. Conventional deflection yokes tend to exhibit undesirably high HSE values for deflecting newer wide deflection angle CRTs.
While certain prior art deflection yokes have employed deflection coils wherein the coils have certain turns arranged for correcting convergence, pincushion distortion and/or other errors, all known prior art deflection yokes employ deflection coils wherein the magnetic field produced by essentially all of the turns thereof affect the electron beams over the entire deflection length of the yoke, although a few turns may be used for certain corrections. Examples include U.S. Pat. Nos. 5,121,028, 5,418,422, and 5,506,469 (e.g., gun-side end turns for correction of mis-convergence, coma errors, astigmatism, north-south raster errors), U.S. Patent 5,077,533 (e.g., screen end turns for modification of third and higher harmonics), and U.S. Pat. Nos. 5,077,533, 5,121,028, 5,418,422 (e.g., side turns for harmonic correction).
It would be desirable to provide greater deflection without increasing the deflection power (or HSE) or to reduce the deflection power (or HSE) required to produce a given deflection, or some combination thereof.
Accordingly, there is a need for an improved deflection yoke and CRT.
To this end, the deflection yoke of the present invention has an exit region between an entrance region and a yoke exit, wherein the exit region is substantially longer than the entrance region, and comprises first and second deflection coils, wherein at least one of the first and second deflection coils has a non-constant distribution of turns in the exit region between the entrance region and the yoke exit of the deflection yoke. A magnetic core is disposed for cooperating with the first and second deflection coils to form a deflection yoke.
According to another aspect, a cathode ray tube comprises a tube envelope, an electron gun providing an electron beam impinging on a screen, and a deflection yoke according to the previous paragraph positioned proximate the tube envelope for scanning deflection of the electron beam produced by the electron gun on the screen.